1. Field of the Invention
This invention relates to a method for producing vinyl chloride resin products which involves sticking vinyl chloride resin members together.
2. Description of the Background Art
Vinyl chloride resin members have conventionally been joined together either by high-frequency fusion welding or with an organic solvent. However, a high-frequency generator and a metallic mold are necessary for high-frequency fusion welding. There is a restriction to the shapes of the portions to be welded together of both members to be joined together because the metallic mold should have such a structure that it covers and presses the portions. Moreover, it is difficult to perform stable and homogeneous high-frequency fusion welding of vinyl chloride resin members because its conditions including high-frequency oscillation and tuning should be adjusted according to the shapes of the portions to be welded together of the members.
When it was impossible to join vinyl chloride resin members together by high-frequency fusion welding because of their shapes or a similar reason, they were stuck together with an organic solvent. The method consists of forming the portions to be stuck together of vinyl chloride resin members into such shapes that the members become in close contact with each other. When the members are not in close contact with each other because of their shapes an auxiliary member is interposed between the members to make them in close contact with each other and then infiltrating an organic solvent into the portions which are in close contact with each other to make surfaces to be stuck together to be dissolved by the organic solvent. For the organic solvent, those capable of dissolving vinyl chloride resins such as tetrahydrofuran (THF), cyclohexanone, ethyl acetate, acetone and methyl ethyl ketone (MEK) are used. In sticking vinyl chloride resin members together with an organic solvent, sufficient ventilation is necessary because of a problem of working environment which is a possibility that the organic solvent evaporates, fills the workroom and adversely affects workers. This leads to a high production installation cost. In addition, despite sufficient ventilation, workers' health conditions have to be periodically confirmed.
Moreover, use of an organic solvent can not avoid its remaining in vinyl chloride resin members. Since an organic solvent is liable to evaporate but has a high affinity for vinyl chloride resins, an excess of an organic solvent used in sticking vinyl chloride resin members together evaporates but not a small amount of the organic solvent dissolves the vinyl chloride resin and infiltrates into it remains in it. The organic solvent remaining in the vinyl chloride resin easily dissolves in an aqueous solution when the thus produced product touches it.
Particularly, when vinyl chloride resin products are those directly touching humor or drug solutions which include blood or solution administration sets, external circulation blood circuits such as dialyzers and pump-oxygenators and catheters, the residual organic solvent will dissolve in humor especially blood or an infusion drug solution thereby entering the patient's body. When vinyl chloride resin products are blood bags or infusion solution bags, as a blood preservation solution or an infusion drug solution contained in the bag touches the inner surface of the product for a long period from its production until its use, there is a high possibility that a residual part of the organic solvent used as an adhesive dissolves in the drug solution. As a result, the organic solvent will be present in the collected blood or the drug solution and when it is administered to a patient the organic solvent will enter the patient's body. As patients requiring blood transfusion or solution infusion usually have reduced physical strength in many cases, entrance of such an organic solvent into the patient's body is very dangerous.
Thus, the object of this invention is to provide a method for producing vinyl chloride resin products which are free from the problems of the method of joining vinyl chloride resin members together by high-frequency fusion welding and the problems of the method of sticking vinyl chloride resin members together with an organic solvent.